Vehicle command systems

ABSTRACT

A command-to-line-of-sight system for controlling guided missiles from an aircraft, in which a two-axis free gyroscope is mounted in the controlling aircraft and maintained as an analogue of a directional reference gyroscope carried in the missile, the analogue gyroscope being mounted in a free gimbal system whose outer free gimbal is pivotally supported by a pair of controlled gimbals. The controlled gimbals are driven by servo mechanisms in response to position signals derived from an optical sight in the controlling aircraft so that the roll axis of the analogue gyroscope is maintained approximately parallel to the line of sight. A compensating signal derived from the analogue gyroscope and representative of roll of the controlling aircraft is supplied to the command signal transmitter in the controlling aircraft and is employed to correct the transmitted command signals so as to compensate for misalignment between the attitude axes of the controlling aircraft and the axes of the missile directional reference system. Alternatively the signal derived from the analogue gyroscope may be employed to maintain the optical image produced by the sight in a fixed attitutde relatively to the aircraft despite roll of the aircraft.

United States Patent 1 Marsh et al.

[ Aug. 21, 1973 VEHICLE COMMAND SYSTEMS [75] inventors: Michael MartinMarsh, Biggleswade;

Geoffrey Thompson, Letchworth; Brian Thomas Trayner, Hitchin, all ofEngland [73] Assignee: British Aircraft Corporation Limited, London,England [22] Filed: May 12, 1971 [21] Appl. No.: 143,714

[30] Foreign Application Priority Data Primary Examiner-Benjamin A.Borchelt Assistant Examiner-Thomas H. Webb Attorney-Cushman, Darby &Cushman [5 7] ABSTRACT A command-to-line-of-sight system for controllingguided missiles from an aircraft, in which a two-axis free gyroscope ismounted in the controlling aircraft and maintained as an analogue of adirectional reference gyroscope carried in the missile, the analoguegyroscope being mounted in a free gimbal system whose outer free gimbalis pivotally supported by a pair of controlled gimbals. The controlledgimbals are driven by servo mechanisms in response to position signalsderived from an optical sight in the controlling aircraft so that theroll axis of the analogue gyroscope is maintained approximately parallelto the line of sight. A compensating signal derived from the analoguegyroscope and representative of roll of the controlling aircraft issupplied to the command signal transmitter in the controlling aircraftand is employed to correct the transmitted command signals so as tocompensate for misalignment between the attitude axes of the controllingaircraft and the axes of the missile directional reference system.Alternatively the signal derived from the analogue gyroscope may beemployed to maintain the optical image produced by the sight in a fixedattitutde relatively to the aircraft despite roll of the aircraft.

9 Claims, 10 Drawing Figures Patented Aug. 21, 1973 7 Sheets-Sheet 1INVENTORS "hung. an. M25 Geovwev mpsm BRIAN T. TRAYNER Pate-atgd Aug.21, 1973 7 Sheets-Sheet 2 INVENTORS MICHAEL M. WARS GEQFFIKEY ThomhsnNBaum T TRflYNER 7 Sheets-Sheet 3 EEEEEEEEEEEEE nN Patented Aug. 21, 1973'7 Sheets-Sheet 5 INV E NTORS (manna. m mus GEOFFREY mom? ON BRHN T.TRAYN Patented Aug. 21, 1973 T Sheets-Sheet '7 FIG. 7A

PR/SM R074 T/UN INC/DENT BEAM EMERGENT B A BEAM ROTATION INVENTORS"\CHEK m, A

GEBFFREY m an: BRIAN 1" 'TRQYNER VEHICLE COMMAND SYSTEMS This inventionrelates to vehicle command systems in which a first vehicle moving inspace is commanded to a line of sight by means of a sighting andguidance system mounted in a second moving vehicle from which the firstvehicle is controlled. The invention is particularly although notexclusively applicable to a command to line-of-sight system forcontrolling a guided missile from a helicopter or ship.

in such systems, the axes of the attitude reference system in the firstvehicle, referred to as the missile, may become misaligned with the axesof the guidance system which is mounted in the controlling vehicle, duefor example to movement of the controlling vehicle, with the result thatcontrol signals transmitted to the missile are in error and the accuracyof guidance of the missile is degraded.

The object of the present invention is to eliminate or reduce such errorby compensating for the movement of the controlling vehicle.

According to the present invention, in a vehicle command system whichcomprises a movable controlling vehicle, a controlled vehicle, referredto as a missile, and means for launching the missile into flight fromthe controlling vehicle and for controlling the flight of the missile bytransmitting command signals from a transmitter in the controllingvehicle to cause the missile to fly along a given line of sight from thecontrolling vehicle, the missile having a flight control systemresponsive to the said command signals and including an attitudereference system, an analogue of the missile attitude reference systemis mounted in the controlling vehicle and is maintained with the axes ofits directional components at the same attitudes in space as the axes ofthe corresponding-components of the missile attitude reference systemboth before and after the instant of launch of the missile and duringits flight, and means is provided for correcting the command signalstransmitted from the transmitter by reference to the analoque referencesystem in the controlling vehicle in such a way as to compensate forchanges in the attitude of the controlling vehicle relative to themissile attitude v reference system after the launching of the missile.

The analogue reference system may comprise a two axis free gyroscopewhose rotor is mounted in inner and outer free gimbals, the outer freegimbal being pivotally supported in a further gimbal system comprisinginner and outer controlled gimbals, servo means being provided formaintaining the controlled gimbals in attitudesin which they support thefree gyroscope with its outer gimbal pivotal axis in a predetermineddirectional relationship with, and approximately parallel to, the saidgiven sight line.

The analogue reference system may include means for deriving a signalwhich represents the angular displacement of the inner controlled gimbalrelatively to the outer free gimbal of the free gyroscope about thepivotal axis of the latter, and means may be provided for utilizing thesaid signal for correcting the command signal to compensate for changesin attitude of the controlling vehicle.

An optical sighting system may be mounted in the controlling vehicle anda manually operated joystick control may be provided for the commandsignal transmitter, the sighting system including means for generatingoutput signals representing its angular displacement in elevation andazimuth from the attitude reference axes of the controlling vehicle, andthe output signals from the sighting system being fed into the servomeans so as to cause corresponding angular displacements of the controlgimbals.

In an arrangement in which the optical sighting system provides a visualimage which shows the missile in flight and the lateral displacement ofthe missile from the sight line, the signal representing relativepivotal displacement of the inner controlled gimbal may be employed tocompensate the command signals for errors caused by the apparent tiltingof the image as seen in the sight relatively to the controlling vehicledue to tilting of the controlling vehicle.

Alternatively, the signal representing angular displacement may beemployed to rotate the image optically, for example by means of a rotaryprism device, so as to compensate for tilting of the controlling vehicleand to maintain the image erect relative to the controlling vehicle andas viewed by an operator therein.

The invention in another form comprises a command system mounted in acontrolling vehicle for controlling a missile carrying an attitudereference system, the command system including in combination atransmitter device for supplying command signals to control the flightof the missile, a mechanical analogue of the missile attitude referencesystem supported in an inner and outer controlled gimbal arrangementmounted in the control vehicle, an electrical pick-off and motor mountedin each of the pivotal axes of support of the inner and outer controlledgimbals, a sighting apparatus mounted in the control vehicle forrotation about first and second axes respectively corresonding to theaxes of pivotal support of the inner and outer controlled gimbals,electrical pickoffs mounted in each of the first and second axes of thesighting apparatus for supplying position signals representative of therotational movements of the sighting apparatus, electrical servo deviceswith position feed-back connecting the pick-offs associated with theaxes of the sighting apparatus to the pick-offs and motors in the innerand outer controlled gimbals, means for activating the analoguereference system and coupling the analogue to the sighting systemthrough the servo devices simultaneously as the missile reference systemis activated by means of a signal used to launch the missile, and a device for correcting the command signals to the missile in a mannerdetermined by an output signal from the analogue reference system tocompensate for movement of the control vehicle.

The invention may be carried into practice in various ways, but twospecific embodiments will now be described by way of example only, withreference to the accompanying drawings in which:

FIG. 1 is a diagram of a control system for a guided missile launchedand controlled from a helicopter,

FIGS. 1A and 1B illustrate diagrammatically the picture displayed by theoptical sight and the corrective movement required of the joystickcontrol in the system of FIG. 1, respectively with the helicopter inlevel flight and when rolled through 45,

FIG. 2 is a circuit diagram of the portion of the control system whichis mounted in the helicopter,

FIG. 3 is an enlarged diagrammatic view of the gimbal arrangements forthe attitude compensating gyro device,

FIG. 4 is a servo diagram of the control system of FIGS. 1 to 3,

FIG. Sis a circuit diagram similar to FIG. 2 of a modified controlsystem, showing the parts which are mounted in the helicopter,

FIG. 6 is a servo diagram of the modified system of FIG. 5,

FIG. 7A is a diagram of the optical prism device provided forde-rotating the picture in the optical sight of the system of FIG. 5,and

FIG. 7B is a diagram illustrating how the rotation of the optical prismthrough 180 rotates the light beam through 360.

In the embodiment of the invention shown in FIGS. 1 to 4 acommand-to-line-of-sight system is provided for controlling a guidedmissile l launched from a helicopter 11. An optical sighting system 12is mounted in the helicopter 11 on a two-gimbalmount 13, being shown inthis case as a simple telescopic sight 12 through which an operator l4sitting in the helicopter can view a target 15. The telescopic sight 12defines a line of sight 16 which the operator aims at the target 15, themissile being visible in the sight as indicated at 10' in FIGS. 1A and1B after it has been launched from the helicopter. The missile 10 isprovided with a receiver and amplifier 17 by which control signalstransmitted from the helicopter after launching are utilized to actuatethe missile fins 18 to control the flight of the missile. The initialcapture of the missile immediately after launching to bring it into thefield of vision of the sight is performed automatically by capturingcontrol means (not shown) which forms no part of the present invention.After the missile has been captured by the automatic capturing controland is directed generally along the line of sight 16 and is visible at10' in the sight 12, the operator controls the flight of the missileonto the target by means of a control unit 20 provided with amanually-operated joystick control 21. The control unit 20 transmitscontrol signals to the missile 10 in accordance with the positioning ofthe joystick control 21, these control signals being transmitted forexample by means of control leads 22 trailed behind the missile inflight, or by a radio link. The operator aims his optical sight 12 atthe target 15 and manipulates the joystick 21 in such a way as to bringthe image 10 of the flying missile as seen in the sight onto the image15' of the target 15 as seen in the sight. These movements of thejoystick control the flight of the missile 10 in such a way as to guideit onto the target 15 by directing the missile along the line of sight16.

The missile 10 is provided with an attitude reference system comprisinga two-axis displacement gyro 25 mounted in gimbals 26, 27 and providedwith electrical picks-offs which supply directional referenceinformation to the missile receiver/amplifier 17. The control signalsfrom the control unit 20 in the helicopter are referred to thedirectional axes defined by the missile reference system 25 to 27, andtheresultant outputs are employed to control the missile.

It will be apparent that as long as the control helicopter remains insteady flight and maintains the same attitude throughout the entireperiod of flight of the missile from launch to strike, the attitudereference axes of the control system in the helicopter will remaincorrectly related to the attitude reference axes in the missile and theguidance signals transmitted from the control unit 20 will correctlycontrol the missile. However the axes of the reference system 25 to 27in the missile are liable to become misaligned with those of the controlsystem in the helicopter, due for example to flight movements of thehelicopter involving attitude changes in roll, yaw and pitch,information of which changes which will not be directly passed to themissile through the radio or wire link 22. As a result of thismisalignment the control signals transmitted to the missile in responseto the movements of the joystick 21 by the operator will be in error,and the accuracy of guidance of the missile will be degraded.

For example, referring to FIG. 1A, assume that the operator is aimingthe sight 12 at a target 15 lying on the fore-and-aft axis of thehelicopter whilst the latter is in steady level forward flight, and haslaunched a missile 10 which has been captured and is visible at 10' inthe sight. Suppose that at a given instant the operator sees the missileimage 10 above the image 15' of the target in the sight, as shown inFIG. 1A, he may then move the joystick control 21 from the centralizedposition 0 to a six-o'clock position A, i.e., immediately towards him,in order to transmit a correcting signal to the missile which will bringthe flight line of the missile towards the line of sight 16 to thetarget.

However, should the helicopter roll through 45 about its fore-and-aftaxis, the picture seen by the operator in the sight will also appear toroll, the horizon tilting through 45, as indicated in FIG. 1B. To bringthe missile image 10' towards the target image 15 the operator wouldexpect to have to move the joystick control 21 not directly towards hisbody to position A but obliquely across his body along a path inclinedat 45 and to a half-past four position indicated at B in FIG. 1B, thedirection O-B corresponding to the direction l0'15 as seen in the sight.However because only the attitude of the helicopter has changed, thecommand signal required to be transmitted to the missile to correct itscourse to the target remains unaltered, and the correct movement of thejoystick 21 to produce this command signal remains O-A, although thismovement no longer corresponds to the direction indicated by the tiltedpicture seen in the sight 12. Hence the operator is required to performa mental operation to compensate for the roll of the helicopter in orderto move the joystick 21 in the proper direction, and this may result inconfusion and incorrect guidance of the missile. Moreover if the roll ofthe helicopter is accompanied by changes of attitude in pitch and/or yawthese will further disturb the alignment between the referencedirections of the control system in the helicopter and the referencedirections of the missile, and will result in increased inaccuracy ofthe control signals.

In order to overcome these difficulties, the portion of the controlsystem which is mounted in the controlling helicopter includes anattitude compensating device 30 mounted in the helicopter l1 and drivenfrom the mounting gimbals of the sight 12. The attitude compensatingdevice 30 comprises a free gyroscope 31 mounted in inner and outer freegimbals 32, 33, the outer gimbal 33 being pivotally mounted about apivotal axis 34 in inner and outer controlled gimbals 35 and 36. Theouter controlled gimbal 36 is pivotally supported by a mounting 37secured to the structure of the helicopter 11. The device 30 acts as anattitude reference system which is employed as an analogue of thedirectional reference system 25, 26, 27 in the missile 10. Thecontrolled gimbals 35 and 36 are driven into transverse and vertical (Xand Y) axes, will automatically ensure that the correct compensationsignal is supplied to the roll angle resolver 51, since the gimbals 35and 36 will drive the pivotal axis 34 of the gyro 31 into parallelrelationship with the line of sight 16 of the sight so that for a givenmanoeuvre of the helicopter the angle of tilt sensed by the pick-off 49for compensation purposes will always be equal to the angle of tilt ofthe picture seen in the sight 12 as a result of that manoeuvre.

As described, the simplest arrangement is that in which the pivotal axis34 of the gyro assembly 31, 32, 33 is maintained exactly parallel withthe line of sight .16. The roll axis of the gathered missile when inflight and under the manual control of the guidance sysmm through thejoystick 21 and control unit, will for minor displacements of themissile from the line of sight 16 be substantially parallel to the lineof sight. For greater displacement of the missile from the line ofsight, when the angle of divergence of the missile roll axis from theine of sight 16 is great enough to be predictable, compensatingpredictions could be fed into the servo loops between the sight 12 andthe attitude compensator device 30 in the form of additional analoguecontrol signals supplied to the inputs of the servo amplifiers 43 and44.

FIG. 4 is a servo diagram of the control system of FIGS. 1 to 3. Asindicated therein, the feedback connection established through the sight12, the attitude compensator device 30 and the roll resolver 51introduces compensation into the signals transmitted from the joystickcontrol 20, 21 through the trailing lead or radio command link to themissile gyro resolver 17, 25, to correct for misalignments between thedirectional reference systems of the missile and helicopter, whichcannot be compensated by any direct mechanical feedback through thecommand link or the optical sighting.

Whilst the optical sight 12 has been described as being a simpletelescopic sight, it will usually be preferable to employ a periscopicsighting system with a mirror system gyro-stabilised in elevation andazimuth, providing automatic compensation for the lateral displacement(usually vertical) of the operators sight line from the optical line ofsight from the periscope to the target. Such stabilised periscopicsights are well known, and normally incorporate electrical pick-offmeans to provide the required output signals proportional to angulardisplacement of the line of sight in elevation and azimuth, for feedinginto the servo loops which control the gimbals 35 and 36 of the device30.

FIGSQS and 6 show a modified embodiment of the invention in which such agyrostabilised peroscopic sight 60 is employed in place of the sight 12of FIG. 1. In this embodiment the required correction for misalignmentsof the attitude reference systems of the missile and helicopter isproduced not by electrically rotating the joystick displacement patternwith respect to the corresponding outputs of the control unit 21 (whichis omitted from FIG. for clarity), but by optically rotating he actualpicture as seen by the operator in the sight 60 to compensate for roll,so that whatever the aerodynamic manoeuvres of the helicopter thepicture as seen by the operator in the sight 60 always remains level anduntilted. This ensures that the appropriate correlation is preservedbetween the direction of the displacement of the missile image from thetarget image 15' as viewed in the sight, and the direction of thecorresonding movement of the joystick 21 required to correct the courseof the missile, so that the operator merely has to move the joystick inthe direction indicated by the picture viewed in the sight. Thearrangement moreover has the advantage that because the picture asviewed in the sight 60 remains always horizontal and untilted, despitetilting of the helicopter, the direction in which the operator has tomove the joystic to effect a given course correction remains constantand does not alter with roll. In other words, whereas as shown in FIGS.1A and 18 it was necessary with the system of FIG. 1 for the operator tomove the joystick from O to A to command a given missile coursecorrection with the helicopter in level flight, but to move the joystickfrom O to B to command the same missile course correction when thehelicopter had tilted and the picture in the sight was tilted; in thesystem of FIGS. 5 and 6 the movement of the joystick required to commanda given course correction from 10' to 15 will always remain a movementfrom O to A regardless of tilted of the helicopter, the picture in thesight remaining horizontal as in FIG. 1A.

The optical rotation of the picture displayed by the periscope sight 60is effected by means of a prism assembly 71 of the kind known as a Doveprism, mounted between the upper and lower mirrors or prisms 72 and 73of the sight in a mounting 74 which is rotatable about the verticaloptical axis 75 between the mirrors 72 and 73. The Dove prism 71 isrotated with its mounting 74 by means of bevel gearing 76 driven by anelectric motor 77. The roll-compensation signal derived from thepick-off 49 of the attitude compensator gyro 31 is supplied to the inputof a servo amplifier 78 the output of which energizes the motor 77 toeffect the required rotation of the Dove prism 61. A pick-off device 79coupled to the spindle 80 of the motor 77 provides positional feedbackto the input of the amplifier 78.

FIG. 6 shows the servo diagram of the embodiment of FIG. 5. This isgenerally similar to that in FIG. 4, except that the compensation fromthe device 30 is applied at the optical sight rather than at thejoystick controller.

FIG. 7A is a diagram showing the Dove prism 61 in side elevation andshowing the optical paths through the prism. Internal reflection of thelight rays occurs at the flank 71A. FIG. 7B is a diagram showing how alight incident light beam in cross-section defined by four parallel raysA B C and D in a square disposition, whilst in the lower row the beam AB C D is shown in the rotated crosssectional orientation in which itemerges from the prism, which is shown in cross-section in foursuccessive rotary positions 45 apart.

Instead of the Dove prism 71, a so-called Pechan prism might beemployed. This is a pair of prisms secured together with a part-silveredsurface at their common face. The rotating effect of the Pechan prism onthe light beam is similar to that of the Dove prism but involves agreater loss of light, incurred by the transmission of the beam throughthe part-silvered common surface.

Whilst in both the specific embodiments described above and illustratedthe control system has employed an optical sight 12 or 60, this could bereplaced by a positions in which they hold the pivotal axis 34 of theouter free gimbal 33 in an orientation which is approximately parallelto the roll axis of the missile in flight. The roll axis 34 may bedirectly parallel to the line of sight 16, or its direction may be afunction of the direction of the line of sight together with otherparameters (such as the rate of turn of line of sight) which can beseparately determined. However for the purposes of clarity, the simplestcase will now be described in which the pivotal axis 34 of the attitudecompensation gyro is driven into parallel relation with the line ofsight 16. For this purpose, the horizontal-axis and vertical-axis gimbalmountings 39 and 40 of the sight 12 in the helicopter 11 are providedwith electrical pick-offs 41 and 42 the output signals of which aresupplied via amplifiers 43 and 44 to electric motors 45 and 46 coupledrespectively to the spindles of the inner and outer controlled gimbals35 and 36, position feedback being provided by electrical positionpick-offs 47 and 48 also on the spindles of the controlled gimbals 35and 36. The output signal from the attitude compensator gyro 31 whichrepresents rotation about the pivotal axis 34 is derived from a furtherpick-off 49 acting between the free outer gimbal 33 and the innercontrolled gimbal 35, and is supplied through a line 50 to the input ofa roll resolver unit 51 whose electrical output is fed into the controlunit associated with the joystick.

As shown in FIG. 2, the system is also provided with a caging controlunit 60 mounted in the helicopter and arranged to be supplied with aninput signal through a line 61 leading from the firing control for themissile. The caging control unit 60 is connectible via a twopole,two-way switch 62 to theinputs of the servo amplifiers 43 and 44 inplace of the sight pick-offs 41 and 42, the switch 62 being actuatedthrough a link 63 by the caging control unit 60. The unit 60 alsoproduces caging and uncaging signals which are transmitted via lines 64and 65 respectively to the missile reference system gyro and to theattitude compensator gyro 31, for the purpose of caging and uncagingthese gyros.

The operation of the system will now be described, as follows. Prior tolaunch, the missile is mounted in a fore-and-aft position in thehelicopter, with its reference gyro 25 caged. The switch 62 is in thecaging position in which it has connected the servo amplifiers 43 and 44to the caging control unit 60 to drive the controlled gimbals intopositions in which the pivotal axis 34 of the free gimbal 33 of theattitude compensator gyro 31 is parallel to the fore-and-aft axis of thehelicopter, and hence also to the roll axis of the missile mountedtherein, and the gyro 31 is caged with its spin axis parallel to that ofthe caged reference gyro 25 in the missile.

When the helicopter 11 is in flight and the caged gyros 25 and 31 arespun up to speed in readiness for launching the missile, the firingsignal is given, the caging control unit 60 transmits uncaging signalsthrough the lines 64 and 65 to uncage the two gyros 25 and 31simultaneously, and at the same time changes over the switch 62 toestablish the servo loops between the optical sight l2 and the attitudecompensator device 30. The output signals of the sight pick-offs 41 and42 cause the motor 45 and 46 to turn the controlled gimbals and 36 anddrive the pivotal axis 34 of the outer free gimbal 33 of the gyro intothe required alignment with the sighting axis 16, e.g., parallel in thesimplest case. The missile is launched, and after launching is gatheredby the automatic gathering control into an alignment in which it isvisible in the sight l2, and subsequent control of the missile iseffected manually by means of the joystick.

Thus the operator aligns the line of sight 16 with the target 15 andmanipulates the joystick control to bring the missile image 10 towardsthe target image 15 viewed in the sight. If the helicopter 11 is level,this requires a movement of the joystick 21 from O to A in FIG. 1A. Ifhowever the helicopter has tilted so that the horizon line appearstilted as viewed in the sight, as in FIG. 1B, the operator moves thejoystick in the direc- 7 tion parallel to the line 10'15 as viewed inthe sight, i.e., from O to B. The tilting of the helicopter will havebeen sensed by the gyro 31 in the attitude compensator device 30, andits pick-off 49 will have provided a compensating signal correspondingto the angle of deflection of the inner controlled gimbal 35 relative tothe gyro-stabilized outer free gimbal 32 of the device 30. The outputsignal from the pick-off 49 is delivered to the roll angle resolver 51,whose electronic circuitry acting in response to the input signalproduces a corresponding variation in the response of the control unit20 to movements of the joystick to compensate for the tilting detectedby the device 30. The action of the roll resolver unit 51 is to produceelectrically a phase rotation between the displacements of the joystick21 and the corresponding output signals of the control unit, therotation corresponding to the tilt angle of the picture as viewed in thesight 12. Thus the correction of the output of the control unit 20 issuch that the movement of the joystick control from O to B in FIG. 18causes the control unit to transmit to the helicopter acourse-correcting signal identical with that produced by movement of thejoystick from O to A in FIG. 1A with the helicopter in level flight.Thus, whatever the angle of apparent tilt of the horizon as viewed bythe operator in the sight, a movement of the joystick 21 in thedirection parallel to the direction 10'15' will always produce acourse-correcting output signal from the control unit 21 compensated bythe roll angle resolver 51 so as to be identical with that produced by acorresponding movement in level flight. The operator is thus always ableto move the joystick control in the direction parallel to that indicatedby the tilted picture seen in the sight, whatever the angle of tilt, andthe system will automatically compensate for the misalignment of thedirectional references due to helicopter attitude changes and willensure that corrected coursecontrolling signals are transmitted to themissile.

It will be apparent that when the sight is directed to a targetimmediately in front of the helicopter so that the line of sight 16 isparallel to the fore-and-aft axis of the helicopter, the angle of tiltof the picture viewed in the sight will equal the angle of roll of thehelicopter. However, when the sight is swung around to follow a targetoff the line of the fore-and-aft axis, or the helicopter moves in pitchand/or yaw, roll of the helicopter will not produce an exactlyequivalent angle of tilt of the picture viewed in the sight 12. Forexample in an extreme case in which the line of sight 16 is directed atright angles to the fore-and-aft axis, roll of the helicopter about thelatter axis will produce zero tilting of the picture seen in the sightas it follows the target.

However, the action of the controlled gimbals 35 and 36, which aredriven in accordance with the components of swivelling movement of thesight 12 about its television sighting arrangement in which a picture ofthe target and flying missile provided by a television camera isdisplayed on a screen to the operator in the helicopter. The operatorfollows the target image on the screen with a gimballed sighting deviceto provide the servo signals to drive the controlled gimbals 35 and 36,and guides the missile onto the target by the joystick control 20, 21.Again, instead of a television system, an automatic tracker might beused, of the ki'nd employing a photoelectric screen which provideselectrical output signals representative of the co-ordinates of thedisplacement from the electrical centre of the screen of an image of themissile (or of a flare carried by the missile) which is focussed on thescreen. In each case the misalignment of the reference systems of thehelicopter and missile due to manoeuvres of the helicopter would becompensated for by means as described, to ensure the transmission ofcorrected command signals to the missile. Moreover a fully automaticsystem may be envisaged, in which the human operator is replaced by anautomatic electronic controller for the transmitter unit 20, theelectrical signals from the television camera or automatic tracker beingsupplied to the controller together with tilt-compensating signals fromthe attitude compensating device 30.

The invention may be employed in other forms of moving craft than ahelicopter, for example aircraft, ships and boats, and land vehicles.

What we claim as our invention and desire to secure by Letters Patentis:

l. A vehicle command system comprising:

a movable controlling vehicle; a controlled vehicle referred to as amissile, and means for controlling the missile in flight after launchingfrom the controlling vehicle including a transmitter transmittingcommand signals from the transmitter in the controlling vehicle to causethe missile to fly along a given line of sight from the controllingvehicle,

the missile including, a flight control system responsive to the saidcommand signals including an attitude reference system,

an analogue reference system of the missile attitude reference systemmounted in the controlling vehicle and maintained with the axes of itsdirectional components in the same attitudes in space as the axes of thecorresponding components of the missile attitude reference system bothbefore and after the instant of launch of the missile and during itsflight, and

means for correcting the command signals transmitted from thetransmitter by reference to the analogue reference system in thecontrolling vehicle so as to compensate for changes in the attitude ofthe controlling vehicle relative to the missile attitude referencesystem after the launch of the missile.

2. A command system as claimed in claim l in which the analoguereference system in the controlling vehicle comrpises a two-axis freegyroscope the rotor of which is mounted in inner and outer free gimbals,the outer free gimbal being pivotally supported in a further gimbalsystem comprising inner and outer controlled gimbals, and servo meansbeing provided for maintaining the controlled gimbals in attitudes inwhich they support the free gyroscope with its outer gimbal pivotal axisin a predetermined directional relationship with, and approximatelyparallel to, the said given sight line.

3. A command signal as claimed in claim 2 including means for deriving asignal from the analogue reference system which represents the angulardisplacement of the inner controlled gimbal relatively to the outer freegimbal of the free gyroscope about the pivotal axis of the latter, andmeans for utilising the said signal for correcting the command signalsto compensate for changes in .attitude of the controlling vehicle.

4. A command system as claimed in claim 3 which includes an opticalsighting system in the controlling vehicle, and a manually-operatedjoystick control for the command signal transmitter, and in which thesighting system includes means for generating output signalsrepresenting its angular displacement in elevation and azimuthrelatively to attitude reference axes of the controlling vehicle, and inwhich the output signals from the sighting system are fed into the servomeans so as to cause corresponding angular displacements of thecontrolled gimbals.

5. A command system as claimed in claim 4 in which the optical sightingsystem includes means for providing a visual image which shows themissile in flight and lateral displacement relative to the sight line,means for compensating the command signals for errors caused by theapparent tilting of the image as seen in the sight in response to asignal representing relative roll displacement of the inner controlledgimbal relative to the controlling vehicle due to roll of thecontrolling vehicle.

6. A command system as claimed in claim 5 in which in response tocommand movements of the joystick control from a centralized position inradial directions the transmitter transmits command signals,representing an analogue of corresponding radial vectors, for correctingthe course of the missile in corresponding radial directions as seen inthe optical sight, and electrical means responsive to the signalrepresenting relative roll displacement of the inner controlled gimbal,is actuated thereby to cause the transmitter output to transmit signalsrepresentative of a relative rotation of the angular phase of the radialvectors, in relation to the phase of the corresponding radial commandmovements of the joystick control.

7. A command system as claimed in claim 4 in which the optical sightingsystem provides a visual image which shows the missile in flight and thelateral displacement of the flying missile from the sight line, and inwhich the signal representing relative angular displacement of the innercontrolled gimbal is employed to rotate the image optically so as tocompensate for tilting of the controlling vehicle and to maintain theimage untilted relatively to the controlling vehicle as viewed by anoperator therein.

8. A command system as claimed in claim 7 in which the signalrepresenting relative angular displacement of the inner controlledgimbal energises a motor which rotatcs an optical prism assemblyinterposed in the light path of the sight to rotate the light beamemerging from the prism assembly about its longitudinal axis, the saidlight beam defining the image as viewed by the operafor.

9. A command system mounted in a controlling vehicle for controlling aguided missile carrying an attitude reference system, the command systemincluding in combination a transmitter device in the controlling vehiclefor transmitting command signals to control the flight of the missile, amechanical analogue reference ill system of the missile attitudereference system supported in inner and outer controlled gimbals in thecontrolling vehicle, an electrical pick-off and motor mounted in each ofthe pivotal axes of support of the inner and outer controlled gimbals,an optical sight in the controlling vehicle which is rotatable about itstransverse axes of support in the vehicle, electrical pick-offs mountedin each of the axes of support of the sight for supplying positionsignals representative of the rotational movements of the sight,electrical servo devices with position feedback connecting the pick-offsassociated with the axes of the sight to the pick-offs and motors of theinner and outer controlled gimbals to form servo loops by which theattitudes of the conafter the launching of the missiles

1. A vehicle command system comprising: a movable controlling vehicle; acontrolled vehIcle referred to as a missile, and means for controllingthe missile in flight after launching from the controlling vehicleincluding a transmitter transmitting command signals from thetransmitter in the controlling vehicle to cause the missile to fly alonga given line of sight from the controlling vehicle, the missileincluding, a flight control system responsive to the said commandsignals including an attitude reference system, an analogue referencesystem of the missile attitude reference system mounted in thecontrolling vehicle and maintained with the axes of its directionalcomponents in the same attitudes in space as the axes of thecorresponding components of the missile attitude reference system bothbefore and after the instant of launch of the missile and during itsflight, and means for correcting the command signals transmitted fromthe transmitter by reference to the analogue reference system in thecontrolling vehicle so as to compensate for changes in the attitude ofthe controlling vehicle relative to the missile attitude referencesystem after the launch of the missile.
 2. A command system as claimedin claim 1 in which the analogue reference system in the controllingvehicle comrpises a two-axis free gyroscope the rotor of which ismounted in inner and outer free gimbals, the outer free gimbal beingpivotally supported in a further gimbal system comprising inner andouter controlled gimbals, and servo means being provided for maintainingthe controlled gimbals in attitudes in which they support the freegyroscope with its outer gimbal pivotal axis in a predetermineddirectional relationship with, and approximately parallel to, the saidgiven sight line.
 3. A command signal as claimed in claim 2 includingmeans for deriving a signal from the analogue reference system whichrepresents the angular displacement of the inner controlled gimbalrelatively to the outer free gimbal of the free gyroscope about thepivotal axis of the latter, and means for utilising the said signal forcorrecting the command signals to compensate for changes in attitude ofthe controlling vehicle.
 4. A command system as claimed in claim 3 whichincludes an optical sighting system in the controlling vehicle, and amanually-operated joystick control for the command signal transmitter,and in which the sighting system includes means for generating outputsignals representing its angular displacement in elevation and azimuthrelatively to attitude reference axes of the controlling vehicle, and inwhich the output signals from the sighting system are fed into the servomeans so as to cause corresponding angular displacements of thecontrolled gimbals.
 5. A command system as claimed in claim 4 in whichthe optical sighting system includes means for providing a visual imagewhich shows the missile in flight and lateral displacement relative tothe sight line, means for compensating the command signals for errorscaused by the apparent tilting of the image as seen in the sight inresponse to a signal representing relative roll displacement of theinner controlled gimbal relative to the controlling vehicle due to rollof the controlling vehicle.
 6. A command system as claimed in claim 5 inwhich in response to command movements of the joystick control from acentralized position in radial directions the transmitter transmitscommand signals, representing an analogue of corresponding radialvectors, for correcting the course of the missile in correspondingradial directions as seen in the optical sight, and electrical meansresponsive to the signal representing relative roll displacement of theinner controlled gimbal, is actuated thereby to cause the transmitteroutput to transmit signals representative of a relative rotation of theangular phase of the radial vectors, in relation to the phase of thecorresponding radial command movements of the joystick control.
 7. Acommand system as claimed in claim 4 in which the optical sightingsystem provides a visual imagE which shows the missile in flight and thelateral displacement of the flying missile from the sight line, and inwhich the signal representing relative angular displacement of the innercontrolled gimbal is employed to rotate the image optically so as tocompensate for tilting of the controlling vehicle and to maintain theimage untilted relatively to the controlling vehicle as viewed by anoperator therein.
 8. A command system as claimed in claim 7 in which thesignal representing relative angular displacement of the innercontrolled gimbal energises a motor which rotates an optical prismassembly interposed in the light path of the sight to rotate the lightbeam emerging from the prism assembly about its longitudinal axis, thesaid light beam defining the image as viewed by the operator.
 9. Acommand system mounted in a controlling vehicle for controlling a guidedmissile carrying an attitude reference system, the command systemincluding in combination a transmitter device in the controlling vehiclefor transmitting command signals to control the flight of the missile, amechanical analogue reference system of the missile attitude referencesystem supported in inner and outer controlled gimbals in thecontrolling vehicle, an electrical pick-off and motor mounted in each ofthe pivotal axes of support of the inner and outer controlled gimbals,an optical sight in the controlling vehicle which is rotatable about itstransverse axes of support in the vehicle, electrical pick-offs mountedin each of the axes of support of the sight for supplying positionsignals representative of the rotational movements of the sight,electrical servo devices with position feedback connecting the pick-offsassociated with the axes of the sight to the pick-offs and motors of theinner and outer controlled gimbals to form servo loops by which theattitudes of the controlled gimbals are controlled in accordance withthe attitude of the sight, means for actuating the analogue referencesystem and coupling the analogue reference system to the sight throughthe said servo loops simultaneously with the activation of the missilereference system in response to a firing signal used to launch themissile from the controlling vehicle, and an attitude compensatingdevice for correcting the command signals to the missile in a mannerdetermined by an output signal from the analogue reference system tocompensate for tilting movement of the controlling vehicle after thelaunching of the missile.